The importance of alkylating substances as carcinogenic and carcinostatic agents makes it desirable to study the mechanism of their action. Although these substances can attack many compounds of biological interest in the cell, the attack on nucleic acids, in particularly deoxyribonucleic acids, has attracted special attention. This interest appears justified because a) The DNA molecules are the heredity determinants of the cell and the mutagenic action of alkylating agents may be caused by their reaction with DNA; in particular, the carcinogenic action of alkylating agents may be a result of such mutagenic action. b) The replication (synthesis) of DNA is a prerequisite for cell division; the carcinostatic action of alkylating agents may be correlated with the interference with replication of DNA. c) Such interference is also known to induce latent viruses; this phenomenon may also occur in the case of oncogenic viruses. The proposed project is the continuation of our fourteen year long research in this field. In the present project we will focus on the influence the cell itself has on the extent and on the effects of DNA alkylation (alkylation in vivo). In particular, it is proposed to study: 1. The effects of the physiological states of the cell (logarithmic and stationary phases); 2. The effects of the genetic states: a) Derepressed (constitutive, induced) vs. repressed (inducible, non-induced) strains; b) Capsulated vs. non-capsulated strains; c) Strains with defective repair mechanisms (sensitive to alkylating agents); d) Strains with impaired repair mechanisms (resistant to alkylating agents); e) Strains carrying episomes. In addition, we will study the possibility of infective transfer of resistance to alkylating agents by the RTF particle (resistance transfer factor). To study the above effects we will determine: 1. The actual extent of alkylation of DNA (7-alkyl guanine produced); 2. The extent of mutagenic action of these alkylating agents, 3. The cell survival; 4. The episome survival ("curing"); 5. Population study to determine survival value in normal media of mutants less resistant or more resistant to alkylating agents, in competition with the parental strains.